His brothers...I wonder how they'll be taking this.
His two elder brothers probably knew they had no chance of ever leading the country; Both brothers are already living carefree lives comparable to Arabian princes, including trips to Disneyland, luxury cars, etc. The third son is really the only one of the three known male "heirs" to seem to take an interest in ruling the country, although whether this is truly by Kim II's design or by the sons' own violition is forever speculation now.
Of course, if he hadn't imposed that atmosphere of terror to that degree, someone might have assassinated him anyway.
I've seen a quote, that says a dictator's greatest victory is to die peaceful of natural causes. Because the only other real options are to be deposed or to be assassinated; despots by definition don't willingly step down.